1. Field of the Invention
The present invention relates to an impact absorber for decelerating a vehicle during a collision with an obstacle by hydraulic damping forces and pneumatic spring forces. The impact absorber has an internal tube and an external tube that are telescopically displaceable one inside the other. The internal tube is closed off to the outside by a base and has a gas space which is subjected to high pressure and interacts with a first liquid space by a separating piston which is axially guided in the internal tube in a sealed off manner. The first liquid space is hydraulically connected via a throttle opening, which is located in an intermediate wall attached inside the internal tube, to a second liquid space bounded by a working piston. The working piston is attached to a piston rod and is guided in the internal tube in a sealing manner and interacts with a third liquid space. A control which can be connected to two chambers is provided to extend the impact absorber assembly or to return it to its normal position.
2. Description of the Related Art
Prior art impact absorbers which employ two tubes that can be displaced one inside the other are known, for example, from DE 40 30 035 A1. In this prior art impact absorber, a gas space is located in an internal tube which is subjected to high pressure and is separated from a first liquid space by a separating piston. The first liquid space is connected to a second liquid space via a throttle point which generates hydraulic damping forces in the normal position, in which the stroke is of such a magnitude as to absorb an impact up to 8 km/h without damage to any parts. In this position, the volume compensation and the rebound of the impact absorber into the normal position are effected by means of a gas cushion prevailing in the closed gas space. A third liquid space is provided which enables the absorption of impact speeds higher than 8 km/h. Pressure can be applied to the third liquid space via a control. Starting from an initial pressure and a basic position, an increase in pressure pushes the external tube and the internal tube apart from one another by a defined axial distance. In the process, a further liquid space is produced between the working piston and a second piston connected to a piston rod. This prior art design involves a high level of construction outlay and requires a large installation space.